Fitting a number of rectangular die on a round wafer typically has a single goal—arranging the die so that as many die as possible can be placed on a single wafer. The die are arranged on the wafer during an exposure process, such as photolithography, and a typical exposure process will use a mask or “reticle”. The reticle will often have 1, 2, or more die, and a reticle is typically exposed or processed at a single time, so that all of the die in the reticle are exposed at one time. The wafer can then be moved to a next location and the group of dies in the reticle are exposed again.
Through trial and error or mathematical algorithm, a determination can be made as to how many dies can be placed on a wafer, and the number of good dies. The number of “good” dies on wafer includes all the dies, excluding those dies that are exposed but will never be fully operational because they are incomplete (e.g., they are only partially on the wafer) and/or they are fatally flawed (e.g., they are located on a beveled edge of the wafer). It is understood that a good die may be incomplete or fatally flawed for other reasons, such as a wafer defect or particle—but a good die has the potential to be a full and functional die.
The present disclosure provides a method for optimizing die placement that goes beyond simply finding the greatest number of good die per wafer. The present disclosure considers other factors, including processing time and peripheral die yield.